Allow users to opt-in to ads to remove 24-hour limit on sync

good.evil.genius says:

Using Remember the Milk on more than one device becomes incredibly problematic with the 24-hour sync limit placed on free accounts. Some of us would like to support the service, but can't afford the extra cost of a pro account currently.

So, I propose that you remove the 24-hour limit for people willing to view ads in the app. This way, you're still generating some income, and you're not giving away all the pro features to non-pro accounts.

Quite frankly, with the 24-hour limit, the app is practically useless.